The invention relates generally to chemical sensors and more particularly to reservoir chemical sensors.
The need for a universal in-situ sensor capable of working with a variety of light interaction techniques (luminescence, absorption, reflection, refraction, Raman and scattering) and using any available sensing chemistry (organic, inorganic, bio-organic, bio-inorganic and genetic) indicates the desirability of an improved reservoir chemical sensor. The sensor should have the capacity to perform qualitative and quantitative analysis, high resolution, long active lifetimes (with both reversible and irreversible chemical interactions) and good reproducibility between sensors for a particular species. The sensing reagents are in liquid form, either liquid themselves, or solids, liquids or gases dissolved in a solvent. The key elements of the sensor can and should be very accurately controlled. The reagent solution can be made with a very high degree of repeatability; the active volume of the reservoir can be precisely controlled and the intensity of the illuminating source and the sensitivity of the detector are accurately known. Reservoir sensors are needed which can incorporate all these features and advantages into a flexible, practical design.
Initial reservoir chemical sensors using fiber optics (reservoir FOCS) are illustrated by U.S. Pat. No. 4,757,343 to Hirshfeld and U.S. Pat. No. 4,666,674 to Miller, et al. which show typical reservoir FOCS formed by attaching a capillary tube coaxially to the end of an optical fiber using a gas bubble or membrane to close the tube. This structure is laborious to assemble accurately, difficult to control and use, and impossible to reproduce uniformly. U.S. Pat. No. 4,892,383 to Klainer, et al and U.S. patent application Ser. No. 503,463 by Klainer, et al. provide an improved reservoir FOCS having a modular design. Although very practical to construct and uncomplicated to use, its applications are restricted by the use of fiber optics to transmit light signals into and out from the sensor to remote sources and detectors.
U.S. patent application Ser. No. 544,681 by Klainer, et al. describes a class of reservoir chemical sensors in which the source and detector are mounted within the cell body, thereby eliminating the need for fiber optics. The reservoir chemical sensor is formed with a modular sensor body which contains a sensing reagent therein in a channel or chamber formed within the sensor body. The species of interest enters into the sensor body through a semi-permeable membrane; alternatively the species may enter through an inlet port. The source and detector are mounted within the cell body itself; protective windows may be used to separate the source and detector from the sensing reagent. This design offers many advantages; however, the reservoir is integral to the sensor body. The sensor can be used for another chemistry, but this requires flushing out the sensing solution, cleaning the cell and replacing with a new sensing solution. If a membrane of different selectivity is required, the membrane must also be replaced. Unless the steps of converting the sensor from one chemistry to another are taken, a plurality of complete sensors, each for a specific chemistry, are required. It would, therefore, be highly desirable to have a reservoir sensor design in which a variety of chemistries can be readily interchanged.